Field of the Invention
The present invention relates to an image processing apparatus, image processing method, and storage medium for printing image data after a quantization process on a print medium using an inkjet print head.
Description of the Related Art
Ink types used for inkjet printing include dye ink containing dye as a color material and pigment ink containing pigment. In general, the pigment ink is superior in light resistance and water resistance to the dye ink, but often inferior in rub resistance. Note that the rub resistance refers to the resistance characteristics of an image printed on a print medium at the time of rubbing the surface of the image. In general, the pigment ink is difficult to permeate into a print medium, and likely to remain on its surface because of its high surface tension, and therefore tends to fix on the surface of the print medium convexly. As a result, when rubbing the surface, a color material is peeled off or moved by friction force, and thereby an image is damaged.
In order to solve such a problem on rub resistance, for example, Japanese Patent Laid-Open Nos. 2005-225948, 2004-131586, and 2006-335858 disclose pigment ink of which rub resistance is improved by making dispersion liquid contain polyurethane resin.
However, even in the case of using ink as disclosed in the above patent literatures, sometimes, sufficient rub resistance cannot be obtained depending on a print state on a print medium.
FIGS. 13A and 13B are diagrams illustrating pigment ink landing states on print media, respectively, each illustrating a cross-sectional view at the time when one or two ink droplets travel toward the print medium, and then land on and permeate into the print medium to form one or two dots. Here, FIG. 13A illustrates a state where one dot lands by itself, and FIG. 13B illustrates a state where two dots land adjacently. In either case of the single dot or the adjacent dots, moisture and a solvent in the ink permeate into the print medium, but a pigment component remains on the surface of the print medium. However, in the case of the single dot, a pigment layer having uniform thickness is formed on the print medium, whereas in the case of the adjacent dots, the thickness of a pigment layer increases in a part where the respective dots overlap each other, and a local convex part is formed. As a result, a state where multiple dots are printed as in FIG. 13B is weak in rub resistance as compared with a state where a single dot is printed as in FIG. 13A.
Meanwhile, the degree of rub resistance varies depending on an ink type. In general, ink having higher surface tension is weaker in permeation force into a print medium, and the rub resistance thereof in an overlapping area as described above is weaker. On the other hand, in the case of ink having relatively low surface tension, rub resistance is unlikely to become problematic. That is, regardless of whether ink to be used is pigment ink or dye ink, the surface tension of the ink is different depending on the type of a color material or a solvent, and the degree of rub resistance is also different.
Also, in the case of using two inks between which the difference in surface tension is large, the permeability of the ink having high surface tension into a print medium can be increased by applying the ink having low surface tension. That is, by printing the ink having high surface tension immediately after or almost simultaneously with printing of the ink having low surface tension, the permeation of the ink having high surface tension can also be facilitated to increase rub resistance.
FIGS. 14A to 14C are diagrams for explaining the effect of such a printing method. FIG. 14A is a landing diagram when an ink droplet of dye ink having low surface tension is applied to a print medium. The dye ink having low surface tension permeates deeply through the print medium, and never remains on the surface of the print medium. FIG. 14B is a landing diagram when immediately after dye ink has landed, pigment ink having high surface tension is applied to the same position. In an area where the dye ink permeates, the fiber of a print medium swells, and the pigment ink containing large particles also easily permeates and is unlikely to remain on the surface. FIG. 14C is a landing diagram when pigment ink and dye inks on both adjacent sides of the pigment ink are simultaneously applied. The pigment ink also becomes likely to permeate through a print medium in association with the dye inks, and as in FIG. 14B, the pigment ink is unlikely to remain on the surface of the print medium. As long as printing is performed in a state like that in FIG. 14B or 14C, unevenness on the surface of a print medium is suppressed, and the rub resistance of an image can be enhanced.
However, the original advantage of pigment ink is to realize a high-density image because pigment remains on the surface of a print medium. Accordingly, preventing pigment from remaining on the surface of a print medium as described above may result in a loss of desired image density.